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      <title>公平锁和非公平锁 - 交互式测验</title>
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            <div class="quiz-header">
              <h1>公平锁和非公平锁 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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      <script>
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  {
    "question": "根据文档，公平锁和非公平锁在处理线程获取锁的请求时，最核心的区别是什么？",
    "options": [
      "公平锁的性能总是优于非公平锁。",
      "公平锁严格遵循“先到先得”的原则，而非公平锁允许新来的线程“插队”。",
      "只有公平锁能有效防止死锁的发生。",
      "非公平锁使用了比公平锁更复杂的队列数据结构来管理线程。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档明确指出，公平锁的核心是保证线程按照请求锁的顺序（先到先得）获取锁，以避免线程饥饿。而非公平锁不保证这个顺序，允许后来的线程“插队”，这可能提高吞吐量，但也可能导致饥饿。这是两者最根本的设计哲学差异。",
    "source": "文档中「基本概念」及「公平锁与非公平锁的比较」-「定义与基本概念」部分",
    "hint": "文档中提到，一种锁策略遵循严格的顺序，而另一种则更加灵活，允许“插队”。"
  },
  {
    "question": "在Java的`ReentrantLock`中，公平锁是如何通过其内部机制保证“先到先得”原则的？",
    "options": [
      "它会立即尝试用CAS操作获取锁，失败后才检查队列。",
      "通过检查等待队列中是否存在比当前线程更早请求的线程（即`hasQueuedPredecessors()`），如果存在，则当前线程必须排队。",
      "它为每个线程分配一个动态的优先级，并按优先级高低授权。",
      "通过随机选择一个等待时间最长的线程来授权。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "公平锁的实现关键在于`hasQueuedPredecessors()`方法。当一个线程尝试获取锁时，会调用此方法检查AQS队列中是否已经有其他线程在等待。如果有，即使锁是可用的，当前线程也不能获取，必须进入队列排队，从而保证了“先到先得”的公平性。",
    "source": "文档中「公平锁的实现」-「锁的获取」及「公平性保障」部分",
    "hint": "思考一下，当一个新线程到来时，公平锁需要做一个什么样的检查来决定是否让它获取锁，而不是直接去抢占。"
  },
  {
    "question": "根据文档描述，当一个线程尝试获取一个非公平锁时，它的首要行为是什么？",
    "options": [
      "首先检查等待队列是否为空，如果为空才尝试获取锁。",
      "将自己加入到等待队列的末尾，并立即进入休眠状态。",
      "直接尝试通过CAS（Compare-And-Set）操作获取锁，而不检查等待队列中是否已有其他线程。",
      "比较自己与队列头部线程的等待时间，以决定是否可以“插队”。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "非公平锁为了追求高吞吐量，其设计允许“插队”。具体实现上，当一个线程请求锁时，它会首先直接尝试通过CAS原子操作来修改锁的状态，试图立即获得锁。只有在这次尝试失败后，它才会进入AQS队列中等待。这就是它“非公平”的体现。",
    "source": "文档中「非公平锁的实现」-「锁的获取流程」部分",
    "hint": "文档中提到，非公平锁在获取锁时会先进行一次“尝试”，这个“尝试”绕过了队列检查。"
  },
  {
    "question": "为什么在许多高并发场景下，非公平锁通常比公平锁具有更高的系统吞吐量？",
    "options": [
      "因为非公平锁的队列管理算法更高效，查找速度更快。",
      "因为公平锁需要消耗更多内存来维护线程的请求顺序。",
      "因为非公平锁减少了线程的上下文切换和调度开销，提高了锁的利用率。",
      "因为非公平锁可以保证所有线程都能在极短时间内获得锁。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档在性能对比部分指出，公平锁严格的排队机制会导致频繁的线程上下文切换（当持有锁的线程释放锁时，需要唤醒队列头部的线程，这个过程涉及调度）。而非公平锁允许一个刚运行的线程立即获取锁，避免了其进入等待状态再被唤醒的过程，从而减少了上下文切换的开销，提升了系统整体的吞吐量。",
    "source": "文档中「公平锁与非公平锁的比较」-「性能对比」部分",
    "hint": "思考线程从运行到等待再到运行的过程，哪种锁策略能有效减少这个过程中的系统开销？"
  },
  {
    "question": "假设你正在设计一个银行的在线交易系统，该系统要求严格按照用户提交请求的顺序处理转账操作。在这种情况下，你应该选择哪种锁，为什么？",
    "options": [
      "应该选择非公平锁，因为它能最大化系统吞吐量，更快地处理所有交易。",
      "应该选择公平锁，因为它能保证线程按请求顺序获取锁，确保交易的公平性和顺序性。",
      "应该选择非公平锁，因为它实现更简单，可以减少代码的复杂性。",
      "应该选择公平锁，因为它能彻底杜绝死锁的发生。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "对于金融交易这类对操作顺序有严格要求的场景，公平性至关重要。公平锁能确保先发起的交易请求先被处理，避免了后来的高并发请求“插队”导致的数据处理顺序混乱。虽然性能可能略低于非公平锁，但业务的正确性和公平性是首要考虑的。",
    "source": "文档中「公平锁的实现」-「应用场景」及「公平锁与非公平锁的比较」-「应用场景」部分",
    "hint": "这个问题的关键在于业务需求：“严格按照……顺序处理”。"
  },
  {
    "question": "在Java中，如果你想使用`ReentrantLock`创建一个默认的、吞吐量优先的锁，应该使用以下哪种方式？",
    "options": [
      "ReentrantLock lock = new ReentrantLock(true);",
      "ReentrantLock lock = new ReentrantLock();",
      "ReentrantLock lock = new NonFairReentrantLock();"
    ],
    "correctAnswerIndex": 1,
    "explanation": "根据文档，Java的`ReentrantLock`类默认实现就是非公平锁。因此，使用无参构造函数`new ReentrantLock()`创建的实例就是非公平锁，这种锁的设计目标是优先考虑系统吞吐量。`new ReentrantLock(true)`则用于创建公平锁。",
    "source": "文档中「非公平锁的实现」-「Java中的配置」部分",
    "hint": "`ReentrantLock`的构造函数在不带参数时，会提供一个默认的公平性策略。"
  },
  {
    "question": "非公平锁相比于公平锁，其最主要的缺点或风险是什么？",
    "options": [
      "系统整体吞吐量会显著下降。",
      "可能导致某些线程长时间无法获取到锁，即产生“线程饥饿”现象。",
      "会引起非常频繁的上下文切换，增加系统开销。",
      "实现逻辑比公平锁复杂得多，容易引入bug。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "非公平锁允许线程“插队”虽然提高了吞吐量，但也带来了风险。如果一个线程运气不佳，在它等待期间，总有新的线程成功“插队”并获取锁，那么这个等待的线程就可能一直得不到执行机会，这种情况被称为“线程饥饿”。这是选择非公平锁时必须权衡的主要缺点。",
    "source": "文档中「非公平锁的实现」-「非公平锁的优缺点」及「公平锁与非公平锁的比较」-「优缺点总结」部分",
    "hint": "想一想，如果一个线程运气不好，总是有新来的线程成功“插队”，它会面临什么问题？"
  }
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            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  